Catheters find particular utility in the medical field where they are used as an instrument for accessing a body cavity, duct, or vessel, to allow drainage or injection of fluids, or access by surgical instruments.
In urinary catheterisation, for example, the distal tip of the catheter is inserted into the urethra of a patient and a balloon is inflated to retain the catheter. Once inserted, the distal tip of the catheter comes into physical contact with the walls of the urethra and/or bladder. During prolonged periods of catheterisation, this contact can lead to bladder cystitis and spasms.
Most conventional urinary catheters use a balloon located around the exterior of the catheter, and stepped back from the distal tip of the catheter, which is inflated once the catheter is in position in order to retain the catheter in place. When it is time to remove the catheter the balloon must be deflated to permit retraction of the catheter. However, all solid materials have a property known as hysteresis. This is a phenomenon where a material is stretched and does not then return to its original state/length. The effect of hysteresis is proportional to the time and degree of stretching. The balloons used on urinary catheters traditionally were made from latex rubber but since it emerged that there was high incidence of latex allergies, silicone balloons were designed. Compared to latex, silicone experiences a higher degree of hysteresis. When urinary catheter balloons are deflated prior to removal, the membrane that forms the balloon folds into a cuff or ridge around the exterior of the body of the catheter. This is a major cause of concern in silicone catheters which have a higher degree of hysteresis, hence larger cuffs. Although the silicone balloons have a higher degree of cuffing/ridging, it should be noted that latex balloons also form the same cuffs but to a lesser extent. The presence of the cuffed balloon results in an increase in both the effective diameter of the catheter, and the friction generated between the cuffed balloon and, for example, the wall of the urinary tract.
Many research articles have addressed the issues and problems related with cuffing. A number of countries including England and Australia have issued safety notices to warn health workers of probable harm/injury that may be caused due to cuffing. A study in Bristol showed that retention forces due to cuffing of urinary catheter were up to 3N, when removing the catheter, due to the friction generated by the cuffed balloon against the inner wall of the urinary tract. All of the studies identified higher incidence of complications in suprapubic catheters, this being due the fact that supropubic tracts are fibrotic and more resistant to stretching.
Another problem experienced with urinary catheter is that they can be blocked due to obstruction by clots, encrustation, prostate chips or lubricating jelly. In current practice blocked catheters are either irrigated with fluid or changed, which exposes patients to higher chances of infection. In intensive care setting if catheterised patients become anuric (don't produce urine), un-necessary catheter changes are done to out rule possible blocked catheter. Further still in patients with prostate or urethral surgery catheter has to remain in situ for a period of at least two weeks, changing the catheter in this period can jeopardise the surgery. However once a catheter does become blocked it is very difficult to unblock.
Removal of the catheter involves deflating the balloon, the deflated balloon usually forming a wrinkled collar structure, also referred to as a “cuff” or “cuffing” around the, normally smooth, outer surface of the catheter. This enlarged and irregular structure impedes retraction of the catheter, and causes discomfort and pain to the patient. Moreover, damage can be caused to the urethral lumen, which increases the risk of acquiring infection.
Indwelling catheters are subject to blockage by, for example, blood clots, debris, and/or crystallisation, requiring irrigation and replacement. This is a time and resource consuming process, which subjects the patient to unnecessary pain, and the stress and anxiety associated therewith. Moreover, the repeated replacement of catheters also greatly increases the risk of infection.
It is therefore an object of the present invention to provide a catheter, which reduces the risk of irritation to the patient, and decreases the discomfort experienced during catheterisation.